1. Field of the Invention
The present invention relates to a novel DNA having a base sequence encoding a glucuronyltransferase. In particular, the present invention relates to a DNA encoding the glucuronyltransferase involved in synthesis of the HNK-1 epitope, which is characteristically expressed on neuronal cells or immune cells.
2. Discussion of Background
Regarding the HNK-1 antigen, which exclusively exists in the nervous system and on immunocytes, it is known that the antigen plays important roles in development of the nervous system and cell adhesion and that peripheral neuropathy attributable to autoimmune disease induces an increase of antibodies against the antigen (Pharmacia, 32, 11, 1361-1369 (1996)). The expression of the antigen by natural killer T cells (NK cells) and the selective attraction by tumor cells of T cells expressing the antigen (Clin. Exp. Immunol., 102, 159-166 (1995)) indicate that the antigen is involved in recognition and elimination of foreign matters by NK cells. However, the HNK-1 antigen expressed on NK cells has been used only as a marker of the NK cells, and its functions are quite unknown. The HNK-1 antigen has 3-sulfated glucuronic acid unlike most glycoproteins and glycolipids, and this structural feature indicates that biosynthesis of the antigen involves a glucuronyltransferase. Glucuronyltransferases are roughly classified into two: glucuronyltransferase-L and glucuronyltransferase-P (J. Biol. Chem., 267, 32, 22711-22714 (1992)), but little is known about these enzymes so far.
As discussed above, the HNK-1 antigen is clearly involved in development and disorder of the nervous system, but their mechanisms have not been elucidated yet. Especially, peripheral neuropathy attributable to autoimmune disease is a serious problem, but development of its curative treatment is retarded. In this respect, clarification of these mechanisms is desired, too. The mechanisms of the recognition and elimination of foreign matters by immunocytes are still unclear, and elucidation of the functions of the HNK-1 antigen is necessary to understand the mechanisms.
For the purpose of elucidating the functions of the HNK-1 antigen, the present inventors successfully extracted and isolated glucuronyltransferase-P (hereinafter referred also to "GlcAT-P") which controls the rate-determining reaction in biosynthesis of the HNK-1 antigen from living tissues, but through complicated procedures and only in small amounts. Further, since cloning of a cDNA of the enzyme had not succeeded, it was impossible to elucidate the functions of the HNK-1 antigen, especially, in living cells.
In view of these problems, for the purpose of earlier elucidation of the functions of the HNK-1 antigen, the present inventors conducted extensive research to obtain the gene of glucuronyltransferase-P which enables mass production of glucuronyltransferase-P which is the enzyme controlling transfer of glucuronic acid, which determines the rate of the synthesis of the HNK-1 antigen in vivo and in vitro and elucidation of the functions of the enzyme. Consequently, they succeeded in cloning of a cDNA of the enzyme and expression of the cDNA as GlcAT-P, and have accomplished the present invention.